Piggy-back hydraulic cylinder provides stroke versatility

Appeared in print as "Piggy-back cylinder provides stroke versatility"

Telescopic cylinders often are favored in telescoping boom lifts and similar long-stroke applications. A multi-stage telescopic cylinder is hard to beat for producing a long extended length from a short retracted length. But when only two stages of extension are needed, a piggy-back cylinder can be a cost-saving alternative and can even add some useful positioning options.

A piggy-back cylinder, manufactured by Texas Hydraulics, Temple, Texas, consists of two standard cylinders with their barrels welded together. In their simplest form, the two cylinders have the same bore and stroke, and a tube connects their cap-end volumes and their rod-end volumes. This simplifies plumbing because only a single hydraulic line is needed for extension and one for retraction, respectively.

The piggy-back cylinder can also be configured to provide four discrete stopping points. This is accomplished by specifying a different stroke for each of the two cylinders and providing independent hydraulic lines for each cylinder. The four stopping points are with both cylinders retracted, with only the shorter cylinder fully extended, with only the longer cylinder fully extended, and with both cylinders fully extended. Other options include an end-mounted block valve, cushions, rod porting, and sequencing.